The present invention relates to mine roof support plates and, more particularly, to a plate of relatively small size adapted to be used within subterranean areas, such as a mine roof. The invention is particularly concerned with such a plate fabricated of stamped sheet steel.
The plate is especially designed for use in mines, tunnels, rock cuts, and other excavations to bind together the various rock strata so as to stabilize the rock formation and prevent its collapse. The plate is intended to be used together with a rock bolt having a conventional bolt anchoring device mounted on its inner end for receipt within a hole bored in the rock to be reinforced. The anchoring device used with the bolt may form a mechanical or chemical anchorage.
The plate of the invention is particularly desirable in that it is of high-strength, lightweight construction and capable of satisfying the requirements of ASTM designation: F 432-76 of the American Society for Testing and Materials. This requires that support plates shall have certain performance deflection characteristics and establishes a test procedure for satisfying these characteristics wherein the plate is first placed over a test plate containing a 4-inch hole and then initially preloaded to 6,000 pounds. Once so preloaded, the load is increased to 15,000 pounds and the bearing plate deflection is measured. The maximum permissible deflection between the 6,000 and 15,000 pound loads is 0.120 inches (3.05 mm.).
The prior art relating to support plates of the type to which the present invention is directed is best exemplified by U.S. Pat. Nos. 3,238,731 and 3,478,523. These patents disclose sheet metal support plates designed to meet a test similar to that of ASTM designation: F 432-76. They are especially concerned with plates having socket-shaped, bolt-receiving recesses designed for use with special bolts having heads with spherical undersurfaces.
U.S. Pat. Nos. 2,748,594; 2,862,368; 3,090,203; 3,163,012; 3,415,064; 3,415,066; and 3,837,258 are also representative of the prior art relating to the present invention. Of these, U.S. Pat. No. 2,748,594 is of particular interest in that it discloses a sheet metal support plate having reinforcing ribs formed therein somewhat like those employed in the plate of the present invention. The plate of the '594 patent is materially different from that of the present invention, however, in that the plate is deliberately designed to deflect upon loading. It is not "rigid" in the same sense as the plate of the present invention and, in all likelihood, could not satisfy the requirements of ASTM designation: F 432-76.